(1) Field of the Invention
The invention relates to a method of checking mask patterns to prevent mask tone errors from causing wafer defects and more particularly to using digital mask data to prevent mask tone errors.
(2) Description of the Related Art
This invention uses digital data describing the clear and dark areas of the masks used in semiconductor wafer manufacturing to check for mask errors before the masks are used in wafer processing. The digital data of different masks is combined in a predetermined manner and the results are checked against expected values. Unexpected results indicate a high probability of mask error.
In U.S. Pat. No. 5,436,097 to Norishima et al. describes a method of mask checking that uses resistance measurements of a conductive film deposited in a test pattern. The test pattern is formed using different rotational orientations and the resistance measurements for the different orientations are compared. This method checks the aligning equipment and the optical system used and is quite different from the method described in this invention.